1 files changed, 88 insertions, 0 deletions
diff --git a/third_party/python/frozenlist/frozenlist/__init__.py b/third_party/python/frozenlist/frozenlist/__init__.py
new file mode 100644
index 0000000000..1ef327bac1
--- /dev/null
+++ b/third_party/python/frozenlist/frozenlist/__init__.py
@@ -0,0 +1,88 @@
+import os
+from collections.abc import MutableSequence
+from functools import total_ordering
+from typing import Tuple
+
+__version__ = '1.1.1'
+
+__all__ = (
+    'FrozenList', 'PyFrozenList'
+)  # type: Tuple[str, ...]
+
+
+NO_EXTENSIONS = bool(os.environ.get('FROZENLIST_NO_EXTENSIONS'))  # type: bool
+
+
+@total_ordering
+class FrozenList(MutableSequence):
+
+    __slots__ = ('_frozen', '_items')
+
+    def __init__(self, items=None):
+        self._frozen = False
+        if items is not None:
+            items = list(items)
+        else:
+            items = []
+        self._items = items
+
+    @property
+    def frozen(self):
+        return self._frozen
+
+    def freeze(self):
+        self._frozen = True
+
+    def __getitem__(self, index):
+        return self._items[index]
+
+    def __setitem__(self, index, value):
+        if self._frozen:
+            raise RuntimeError("Cannot modify frozen list.")
+        self._items[index] = value
+
+    def __delitem__(self, index):
+        if self._frozen:
+            raise RuntimeError("Cannot modify frozen list.")
+        del self._items[index]
+
+    def __len__(self):
+        return self._items.__len__()
+
+    def __iter__(self):
+        return self._items.__iter__()
+
+    def __reversed__(self):
+        return self._items.__reversed__()
+
+    def __eq__(self, other):
+        return list(self) == other
+
+    def __le__(self, other):
+        return list(self) <= other
+
+    def insert(self, pos, item):
+        if self._frozen:
+            raise RuntimeError("Cannot modify frozen list.")
+        self._items.insert(pos, item)
+
+    def __repr__(self):
+        return '<FrozenList(frozen={}, {!r})>'.format(self._frozen,
+                                                      self._items)
+
+    def __hash__(self):
+        if self._frozen:
+            return hash(tuple(self))
+        else:
+            raise RuntimeError("Cannot hash unfrozen list.")
+
+
+PyFrozenList = FrozenList
+
+
+try:
+    from ._frozenlist import FrozenList as CFrozenList  # type: ignore
+    if not NO_EXTENSIONS:  # pragma: no cover
+        FrozenList = CFrozenList  # type: ignore
+except ImportError:  # pragma: no cover
+    pass